If possible, you can catch the feet with your hands to pull your chest closer towards the toes. To keep the lower back as long as possible, keep reaching your heart out past the feet. This is not something you can physically accomplish, but it keeps your mind present and your body focused on continuing to create length.
Drop your nose down to face your shins, if you have the range of motion, the head can even rest on the legs. Hold here for as much time as is comfortable for you. This is a very common yoga pose and stretch for the hamstrings; you will see the most physical result when you are warmed up but this is a pose you can do at anytime and feel a nice quieting sensation in the body and mind.